Cross-linked insoluble product

The most widely used synthetic access to these materials begins with very pure (NPC12)3 from which all PC15 has been eliminated. Failure to eliminate all PC15 leads to a cross-linked, insoluble product not suitable for further chemistry. When (NPC13)3 is heated above 230°C it gives the polymer, where the degree of polymeriza-... 

Copolymerizations involving dienes such as the copolymerization of isobutylene with isoprene are important from the industrial point of view (3,4). Isoprene acts as a strong chain-transfer and terminating agent in the carbocationic polymerization of isobutylene (161), and at high concentration it leads to a cross-linked, insoluble product (180). Because of the limited composition range available for analysis, determination of the reactivity ratios in this system is rather difficult. Reactivity ratios published for the isobutylene/isoprene system are listed in Table 7. 

Fortenberry and Pojman studied FP of acrylamide in detail.Synthesis of polyacrylamide via FP resulted in a cross-linked, insoluble product. Figure 12 shows that the maximum... 

The structure of polymer [20] was confirmed by infrared spectral analysis (99). Spectral evidence indicated that more than 90% of the monomer units were consumed via cyclopolymerization. However, polymerization in bulk or emulsion yielded cross-linked insoluble product only. 

A number of modifications of the structure of the allylstannane have been prepared with the aim of facilitating the removal of tin from the product. These include Curran s fluorous allylstannane (see Section 3.14.04.1), Pereyre s monoallylstannane AllylXSn[N(TMS)2]2 (Equation (92) above),258 allylstannanes with a polar (oligoethylene oxide) tail (e.g., 23 and 24), and the allylstannyl group bonded to a soluble or insoluble (cross-linked) polystyrene. The reaction using the allylstannane bonded to a soluble, uncross-linked, polystyrene resin occurs about 100 times faster than that on the cross-linked, insoluble resin, and the polymer can be recovered by recrystallization from methanol. 

Since the only by-product is hydrogen, the purification of the precursors can be performed by evaporating all volatile components from the reaction mixture. The catalyst used remains in the precursor. An important advantage over ammonolysis reactions of chlorosilanes is the possibility of synthesizing highly cross-linked insoluble polymeric precursors, which are usually difficult to separate from solid by-products. 

In all the runs, the formation of brown solid films was observed on the reactor wall or on the surface of the grains. These solid films were not analyzed but they were insoluble in methyl ethyl ketone or toluene. It is presumed that these films are probably highly cross-linked polymerized products derived from the cresol. The energy yield for film formation was estimated to be in a range from 30 to 50 gram/kwh. considerably higher than that for the fragmentation products. 

The observed high cyclization is attributed to an interaction between the double bonds in the transition state, since a strong bathochromic shift of the absorption due to the double bonds is observed in the uv spectrum. Six-membered rings as well as five-membered rings have been observed experimentally in the polymerization of 1,6 dienes. As expected, the extent of cyclization in this case depends strongly on the thermodynamic quality of the solvent (Table 16-10). In such polymerizations, soluble products are obtained, even at highest yields, because of the strong cyclization, whereas extensive reaction as for Equation (16-54a) would lead to cross-linked, insoluble polymers. 

Should branching become excessive, infinite networks can form. The products become cross-linked, insoluble, and infusible. Such materials are called popcorn polymers. This phenomenon is more common in bulk polymerizations. The cross-linked polymers form nodules that occupy much more volume than the monomers from which they formed and often clog up the polymerization equipment, sometimes even rupturing it. 

Condensed phosphoramides with linear, cyclic, or cross-linked structures are produced by the reaction of POCI3 with ammonia. The higher molecular weight products are insoluble in water and on fnrther heating are converted to a cross-linked insoluble polymer, phosphorus oxynitride (PON)j (25). Phosphorus oxynitride can be made by prolonged heating of melamine phosphates (26), urea phosphate (26), or ammonium phosphate imder conditions where ammonia is retained (27). Phosphorus oxynitride is an effective flame retardant in those polymers, such as nylon 6, which can be flame retarded by exclusively char-forming condensed-phase means. However, phosphorus oxynitride is ineffective (at least by itself) in those... 

Park et al. investigated the influence of the structure of the polymer on the activity of PS-immobilized IL [50]. They immobilized ammonium-based IL on three types of chloromethylated PS (FSl, PS2, and PS3), and used the immobilized IL catalysts for the reaction of CO2 and glycidyl methacrylate. PSl is a soluble copolymer prepared from ST and VBC. Both PS2 and PS3 are the cross-linked (insoluble) copolymers prepared from ST, DVB, and VBC, but the latter had macropores which were generated by addition of isooctyl alcohol to the mixture of ST, DVB and VBC before the copolymeiization and the consecutive extraction of the alcohol by methanol after the pwlymerization. The product yield depended on the structure of the support polymer. It was in the order of PSl > PS3 > PS2, which could be expected by considering the accessibility of the substrates to the IL active site. 

Some commercially important cross-linked polymers go virtually without names. These are heavily and randomly cross-linked polymers which are insoluble and infusible and therefore widely used in the manufacture of such molded items as automobile and household appliance parts. These materials are called resins and, at best, are named by specifying the monomers which go into their production. Often even this information is sketchy. Examples of this situation are provided by phenol-formaldehyde and urea-formaldehyde resins, for which typical structures are given by structures [IV] and [V], respectively ... 

Melamine resins were introduced about ten years after the Beetle molding compound. They were very similar to those based on urea but had superior quaHties. Henkel in Germany was issued a patent for a melamine resin in 1936 (7). Melamine resins rapidly supplanted urea resins and were soon used in molding, laminating, and bonding formulations, as well as for textile and paper treatments. The remarkable stabiHty of the symmetrical triazine ring made these products resistant to chemical change once the resin had been cured to the insoluble, cross-linked state. 

Divinylbenzene. This is a specialty monomer used primarily to make cross-linked polystyrene resins. Pure divinylbenzene (DVB) monomer is highly reactive polymericaHy and is impractical to produce and store. Commercial DVB monomer (76—79) is generally manufactured and suppHed as mixtures of m- and -divinylbenzenes and ethylvinylbenzenes. DVB products are designated by commercial grades in accordance with the divinylbenzene content. Physical properties of DVB-22 and DVB-55 are shown in Table 10. Typical analyses of DVB-22 and DVB-55 are shown in Table 11. Divinylbenzene [1321 -74-0] is readily polymerized to give britde insoluble polymers even at ambient temperatures. The product is heavily inhibited with TBC and sulfur to minimize polymerization and oxidation. 

Highly cross-linked polyol polytitanates can be prepared by reaction of a tetraaLkyl titanate with a polyol, such as pentaerythritol, followed by removal of the by-product alcohol (77). The isolated soHds are high activity catalysts suitable for use in the preparation of plasticizers by esterification and/or transesterification reactions. The insoluble nature of these complexes faciUtates their... 

Because enzymes can be intraceUularly associated with cell membranes, whole microbial cells, viable or nonviable, can be used to exploit the activity of one or more types of enzyme and cofactor regeneration, eg, alcohol production from sugar with yeast cells. Viable cells may be further stabilized by entrapment in aqueous gel beads or attached to the surface of spherical particles. Otherwise cells are usually homogenized and cross-linked with glutaraldehyde [111-30-8] to form an insoluble yet penetrable matrix. This is the method upon which the principal industrial appHcations of immobilized enzymes is based. 

In Ancient Egypt mummies were wrapped in cloth dipped in a solution of bitumen in oil of lavender which was known variously as Syrian Asphalt or Bitumen of Judea. On exposure to light the product hardened and became insoluble. It would appear that this process involved the action of chemical cross-linking, which in modem times became of great importance in the vulcanisation of rubber and the production of thermosetting plastics. It was also the study of this process that led Niepce to produce the first permanent photograph and to the development of lithography (see Chapter 14). 

Of the various amino-resins that have been prepared, the urea-formaldehyde (U-F) resins are by far the most important commercially. Like the phenolic resins, they are, in the finished product, cross-linked (thermoset) insoluble, infusible materials. For application, a low molecular weight product or resin is first produced and this is then cross-linked only at the end of the fabrication process. 

In addition to the insoluble polymers described above, soluble polymers, such as non-cross-linked PS and PEG have proven useful for synthetic applications. However, since synthesis on soluble supports is more difficult to automate, these polymers are not used as extensively as insoluble beads. Soluble polymers offer most of the advantages of both homogeneous-phase chemistry (lack of diffusion phenomena and easy monitoring) and solid-phase techniques (use of excess reagents and ease of isolation and purification of products). Separation of the functionalized matrix is achieved by either precipitation (solvent or heat), membrane filtration, or size-exclusion chromatography [98,99]. 

By replacing insoluble cross-linked resins with soluble polymer supports, the well-estabhshed reaction conditions of classical organic chemistry can be more readily apphed, while still fadhtating product purification. However, soluble supports suffer from the hmitation of low loading capacity. The recently introduced fluorous synthesis methodology overcomes many of the drawbacks of both the insoluble beads and the soluble polymers, but the high cost of perfluoroalkane solvents, hmitation in solvent selection, and the need for specialized reagents may hmit its apphcations. 

The catalysts mentioned above are soluble. Certain cross-linked polystyrene resins, as well as alumina and silica gel, have been used as insoluble phase-transfer catalysts. These, called triphase catalysts, have the advantage of simplified product work up and easy and quantitative catalyst recovery, since the catalyst can easily be separated from the product by filtration. 

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